Low carbon high strength steels which exhibit a minimum yield strength of 75,000 psi, and/or a minimum tensile strength of 85,000 psi. together with acceptable ductility are increasingly in demand.
Some prior art steels require heating, quenching, and tempering treatments subsequent to rolling before they can exhibit such properties. Such treatments are undesirable from the standpoint of cost and efficiency.
Some prior art steels which can exhibit high as-rolled strength require the presence of at least 0.07 weight percent of carbon plus other strengthening agents such as chromium.
One such low carbon high strength steel and its method of manufacture is found in U.S. Pat. Nos. 3,689,259 and 3,544,393 issued to Joseph R. Zanetti on Sept. 5, 1972 and Dec. 1, 1970, respectively. The steel disclosed in these patents requires at least 0.07 weight percent of carbon plus chromium, columbium, boron and zirconium strengthening agents. Unless otherwise noted, all composition percentages hereinafter are weight percent. Each additional strengthening agent adds to the cost of such steel, especially chromium which is becoming increasingly difficult to obtain.
There is a need therefore for a low carbon steel, having not more than 0.07% carbon, which steel exhibits in the as-rolled condition high yield and tensile strength plus acceptable ductility and toughness with a minimum of strengthening agents and preferably with no chromium. There is also a need for a method for producing such steels.